Augmented reality applications allow a user to see a presentation of the world augmented with or superimposed by computer-generated content. The content may be graphical, textual, and/or audible. The presented world may be presented directly to the user, such as when the user is looking through a display, and the imagery is applied to or projected on the display. The world may also be presented indirectly, such as when a user is navigating previously captured images of the real world, rather than the world that is presently in front of the user.
A head mounted display (“HMD”) is a display device worn on or about the head. HMDs usually incorporate some sort of near-to-eye optical system to emit a light image within a few centimeters of the human eye. Single eye displays are referred to as monocular HMDs while dual eye displays are referred to as binocular HMDs. Some HMDs display only a computer generated image (“CGI”), while other types of HMDs are capable of superimposing CGI over a real-world view. This latter type of HMD can serve as the hardware platform for realizing augmented reality. With augmented reality the viewer's image of the world is augmented with an overlaying CGI, also referred to as a heads-up display (“HUD”), since the user can view the CGI without taking their eyes off their forward view of the world.